This invention relates to a heavy load pneumatic tire. More particularly, it is concerned with a block pattern formed on a tread by circumferentially extending longitudinal grooves and transverse grooves extending axially of the tire, and provides an all-season tread pattern having an improved groove depth and width which can be used at any time of the year throughout the winter and summer seasons.
A pneumatic tire usually has a tread pattern of the lug, rib, rib-lug, block, lug-block or rib-block type, depending on the use of the tire, seasonal factors, road conditions, etc.
For example, a tire of the rib type has a plurality of ribs defined by a plurality of circumferentially continuous grooves which divide a tread surface across its width. The tread pattern of such a rib tire makes it suitable mainly for traveling on a good road at a high speed. It has, therefore, been playing an important role as a tire for, for example, a highway bus, long-distance truck or sightseeing bus. The block pattern is composed of blocks of various shapes defined by a multiplicity of notches in a tread surface. The edges of the notches catch the road surface firmly, and enable a great improvement in coefficient of traction power and transverse sliding resistance. They serve only effectively for drainage purposes on a wet road, and exhibit an excellent wet grip and a high performance on snow.
By virtue of these features, a tire having a block tread pattern is particularly used during the rainy season or when it has snowed, replacing tires of other types whenever required.
The remarkable development which Japan has recently achieved in its highway network, however, has come to compel trucks or buses to travel over a greatly increased distance. Such a change in the mode of vehicle operation tends to bring about a greater variety of requirements for tires. As a single drive covers a long distance, it is likely that the vehicle may encounter many changes in weather and road conditions (the road may be a local one, a highway or an unpaved, snow-covered, frozen or wet one). There is, therefore, a strong demand, especially from the industry handling large trucks and buses, for a tire which enables a long time of continuous traveling, irrespective of any such changes in weather and road conditions.